Efficiency Factors?

What are some important factors that account for mash efficiency? On my last mash I did about 90% efficiency vs the usual 72%. Obviously, I'd like to get 90% every time, but I don't know what I should adjust. Things different from previous brews were mash ratio (1.5qts/lb), rest temperature (I usually do both a beta amylase/limit dextrinase rest and an alpha amylase rest, but this time I did a single rest at 149F), and mash pH (added slightly over half a pound of acidulated malt). Are any of those things more likely than the others to increase efficiency by so much?

Beer Trader

72% to 90%. Seems unlikley to me that those changes would have caused that big a jump. When did you measure your gravity for the purpose of computing your efficiency, and did you take the actual (vice planned) volume into consideration? It might also help if you post your grain bill and measurements.

The two things that most impact mash efficiency are mash thickness and mashing temperature. A thinner mash (e.g., 2 quarts/lb.) will result in greater efficiency. For an infusion mash a higher temperature will result in greater efficiency.

Other factors which can effect efficiency to a lesser extent is mash time and the amount of grain crush (mill gap setting).

The maximum extract potential for that grain bill should have been about 1.072, but I was targeting 1.052 for 5.5 gallons assuming my efficiency would be about 72%. I took gravity readings several times, but the moment I realized something was really different is when I added a little too much sparge water to the boil, took a gravity reading, and the gravity was much higher than expected. I reached the target gravity after boiling down to 7 gallons. So to figure out where my gravity would be if boiled down to the intended 5.5 gallons, I figured:
(52x7)/5.5 = 66.2
and for percentage of maximum yield, 66.2/72 = 0.91 (91%)

The grist ratio usually depends on what style I'm making, but, for example, I last brewed a doppelbock with a ratio of 2qts/lb, and still only managed 72%

Is this regardless of time or do you mean that a higher temp will result in higher efficiency, given some constant mash time? (My understanding was the latter, and that a longer mash basically erases the efficiency advantage.) Also, is it in that link somewhere? I love Kai, but sometimes the reader's digest version would be nice.

In Kai’s ‘paper’ he has a graph of Efficiency vs. Mash Time for two mash temperature: 67°c and 72°C. The efficiency is greater for a mash temperature of 72°C vs. 67°C.

Below is the Conclusion part of his paper:

“Attenuation and efficiency of the mash are effected by many mash parameters. Some have more impact others have less. When using a single infusion mash, temperature and time are the best parameters that a brewer can work with to target a specific fermentability of the wort. The time should be long enough to allow for complete conversion of the mash or at least a wort that doesn't contain any starch (negative starch test). This might be achieved after 15-30 min, but a longer mash rest may be needed to achieve the desired fermentability. The mash pH should always be controlled and kept between 5.4 and 5.7 when measured at room temperature (5.05 - 5.35 when measured at mash temperature). This pH control can be done through the brew water design (residual alkalinity) and/or acid/salt addition to the mash.

Brewers that don't mill their own grain will not be able to effect the tightness of the crush and will have to accept lower conversion efficiencies or ensure that the mash has enough time and "strength" to achieve an acceptable conversion of the starches. If the mill gap spacing can be controlled the conversion efficiency can be improved through a tighter crush. But at some point the crush might be to tight for a resonable run-off speed.

The thickness of the mash doesn't seem to effect the fermentability of the wort that is produced but thinner mashes can significantly improve the conversion efficiency. As a result brewers who see low efficiency from their mashing may try to use a thinner mash (3-4 l/kg or 1.5 - 2 qt/lb) as they were shown to convert more starches.

When working with large amounts of highly kilned malts attenuation and efficiency problems can arise due to the lower diastatic power (enzymatic strength) of these malts. This can be counteracted by lower mash temperature and longer mashes or the addition of a diastatic stronger malt to the grist (e.g. 10-20% of Pale/Pilsner malt)

While the water composition may also have an impact on attenuation and efficiency besides the change in mash pH through the residual alkalinity, its impact is considered small and secondary.”

Beer Trader

Using some assumptions for PPG for those grains (without knowing specific maltsters), my calculations also put you right around 90% efficiency for 1.052 in 5.5 gallons. Two other things that comes to mind...

- did you weight those grains yourself? If not, I'm wondering if there could have been more grains than you thought/ordered.

- did you crush the grains? If not, is it possible that these grains were crushed more finely than for your previous batches?

Edit: two more thoughts...
- was that 7 gallons in the kettle measured hot, but the gravity from a sample measured at room temp?
- Your oversparging would have caused a higher efficiency. How much 'too much' sparge water did you use?

Beer Trader

What are some important factors that account for mash efficiency? On my last mash I did about 90% efficiency vs the usual 72%. Obviously, I'd like to get 90% every time, but I don't know what I should adjust. Things different from previous brews were mash ratio (1.5qts/lb), rest temperature (I usually do both a beta amylase/limit dextrinase rest and an alpha amylase rest, but this time I did a single rest at 149F), and mash pH (added slightly over half a pound of acidulated malt). Are any of those things more likely than the others to increase efficiency by so much?

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Efficiency is important to breweries. Better efficiency means lower cost of production. But the process that one would have to go through to achieve 90% efficiancy would probably be detrimental to most homebrewers - not worth the return.

Beer Trader

In Kai’s ‘paper’ he has a graph of Efficiency vs. Mash Time for two mash temperature: 67°c and 72°C. The efficiency is greater for a mash temperature of 72°C vs. 67°C.

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Ah. Thanks, I see that chart now. I would note that 72C is about 162F, which is well above the normal range of mash temps. My first guess would be that at 162F, full converion is just starting to lose the race against the denaturing of enzymes.

- did you crush the grains? If not, is it possible that these grains were crushed more finely than for your previous batches?

Edit: two more thoughts...
- was that 7 gallons in the kettle measured hot, but the gravity from a sample measured at room temp?
- Your oversparging would have caused a higher efficiency. How much 'too much' sparge water did you use?

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Yeah, weighed them myself, crushed them myself, just the same as usual. The gravity reading at 7 gallons was allowed to cool to 60F, and I probably sparged with a little over a half gallon more than intended.

Efficiency is important to breweries. Better efficiency means lower cost of production. But the process that one would have to go through to achieve 90% efficiancy would probably be detrimental to most homebrewers - not worth the return.

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That's the thing though, I didn't do anything out of the ordinary.

I guess here's hoping I can do that consistently. Maybe the cause will become more apparent in the future.

Beer Trader

The gravity reading at 7 gallons was allowed to cool to 60F, and I probably sparged with a little over a half gallon more than intended.

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Okay, so I think there are at least two contributors identified...
1) oversparging
2) Your 7 gallons at boiling (or near boiling) temp is more like 6.7 gallons at 60F. So your calculated 91% efficiency drops to a little under 88%. Not a huge difference, but closing the gap a bit.

Subscriber

Kia's conclusions aren't exactly clear and should probably be expanded on. When looking at his data it shows the the biggest jump in efficiency is due to mill gap and he stops at 0.035". Which makes sense to me. Everything I've ever read has stated that the most significant factor for efficiency is the crush. And that's been my experience as well. You should always start with crush when trying to solve big jumps in efficiency in either direction. (after you are positive you've made no errors in calculations or measurements).

Randy Mosher (I forget which book) has a nice table on the factors that impact mash efficiency and to what extent. I'll see if I can find it and post.

To the OP, did you crush with your own mill or at the LHBS? If at the LHBS, the gap could have changed. If your own mill, did you change the gap? Clean the rollers? Do something that might have changed the gap?
The gap doesn't have to be off much to make a significant difference in efficiency.

FWIW: My efficiency was kind of all over the place before I started paying attention to mash pH. This probably had more impact in my case than in most since I use adjusted RO water, but it seems to account for a gain in efficiency for me from about 70% to 80% or more in recent mashes. If you weren't previously adjusting for pH, perhaps that accounts for some of the increase.

Something you'll notice on a homebrew scale are that efficiency doesn't matter as much as consistency. So what if you save a pound of base malt? It might take you an extra hour to fly sparge to get 90% efficiency. There is strong argument that 60% efficiency gives you the best 60% of the malt flavor. The rest degrades the quality of the beer. There are lots of factors here. Time, cost, equipment for fly sparging, crush, sanity etc. that you should take into consideration. I think anything around 70-80% is totally acceptable and I don't have to adjust my recipes out to the thousandth of an ounce.

Ray Daniels Designing Great Beer mentions a large number of award winning brewers used malt extract at some point in their recipes. Off the top of my head it's like 2/5 to 3/5 of his poll. So even on the upper end, there's room for adjustment.

Kai stated: “The tighter the crush, the higher the brewhouse yield. But the difference between a 0.35 mm(13 mil) crush and a 0.95 mm (37 mil) crush was only about 10%.”

With regards to mash thickness: “A significant difference was however found in the efficiency. The brewhouse efficiency of the thick mashes remained almost constant between 58 and 60% over the temperature range of the experiments, but the brewhouse efficiency for the thinner mash showed a strong dependency on the temperature and was always better than the efficiency of the thick mash. That leads to the conclusion that thinner mashes perform better and allow for better extraction of the grain.” The difference between 68% and 60% is 13.33%.

With regards to mash temperature (and 60 minutes of mash time):

· At 72°C he got an efficiency of 68%· At 67°C he got an efficiency of 57%

The difference of the two above efficiencies is 19.3%.

The test range of the mill gap setting seems a bit strange to me. Does anybody crush their grains even close to the 0.35 mm (13 mil)? I would think that this would result in grain that is too finely crushed for effective sparging.

So, it seems to me that based upon Kai’s experiments that the two biggest factors for increasing efficiency is mash temperature (higher mash temperature) and mash thickness (thinner mash).

if you fly sparge (as opposed to batch sparging), pay close attention to the speed at which you lauter. If you lauter too fast you'll get channeling within the grain and leave too much sugar behind. Try to stick to two minutes per quart.

2) Your 7 gallons at boiling (or near boiling) temp is more like 6.7 gallons at 60F. So your calculated 91% efficiency drops to a little under 88%. Not a huge difference, but closing the gap a bit.

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Ahhh thermal expansion. I hadn't even thought of that. Well anyway, all your input is really helpful. I crush at my LHBS, so I'm sure something changed. I'm willing to bet that has a lot to do with it.

Now that sounds more promising. Do you have a link to this? I've been looking for something that compares mash temp (multiple temps in normal mash temp range) to mash efficiency, where the time before full conversion isn't constrained.

I will no longer respond to queries about Kai’s experiments. If folks have additional questions or concerns about the experiments that Kai conducts it would be appropriate to direct your queries directly to Kai since he is the source of the information.

Subscriber

Jack thanks for those links, also this response is not directed at you or Kai, I just wanted to add more comments. I do agree that temperature is a significant factor that affects efficiency, but I don't consider it a 'lever' that is necessarily available for increasing efficiency. I don't think a brewer will adjust mash temps for efficiency's sake, they adjust it for the level of fermentability they want. The mash out temps will help efficiency, but that again is a choice the brewer makes. I don't always mash out.

That being said 'crush' is a lever that can be used to increase efficiency. And a grist comprised of flour and hulls is ok as long as you can lauter properly. IMO Kai stopped short on exploring mill gap, mill gaps can be tighter than 0.035", for instance I set mine to 0.030". He may have stopped at 0.035" because that is more of a practical limit for the type of mill homebrewers have access to. And IMO thats always a wild card when using a mill at the LHBS, you know know what it is set to unless you adjust it yourself.

This may be a stupid question, but if you end your mash with a lower than anticipated gravity/efficiency, would adding extra sparge water and then boiling longer to get to your target volume work to compensate? I'm far from a scientifically-minded brewer but the water would boil off/evaporate and leave a higher concentration of sugars right?

Beer Trader

This may be a stupid question, but if you end your mash with a lower than anticipated gravity/efficiency, would adding extra sparge water and then boiling longer to get to your target volume work to compensate?

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Yes. But another question would be whether the longer boil is a worthwhile solution, both in terms of time and in terms of extra melanoidin formation (which you may not want). I'd say that most people who want to increase the gravity of a disappointing mash probably add DME.

Yes. But another question would be whether the longer boil is a worthwhile solution, both in terms of time and in terms of extra melanoidin formation (which you may not want). I'd say that most people who want to increase the gravity of a disappointing mash probably add DME.